Machine adjustable boring bars have previously been suggested, and among the first types were ones wherein a radial adjustment of the boring tool was possible, yet the tool holder was not interchangeable, i.e., it was generally a permanent part of the machine tool spindle. One of the first which achieved radial adjustment of the boring tool by means of a drive shaft was disclosed in U.S. Pat. No. 2,945,401. A longitudinally movable central rod was suggested for use in the radial adjustment of a boring tool in U.S. Pat. No. 3,740,161. An internal electric servomotor was suggested for this purpose in U.S. Pat. No. 3,237,486. A stylus and a contoured template were suggested for this purpose in U.S. Pat. No. 3,802,304. U.S. Pat. No. 3,822,618 disclosed a contour cam for this purpose. U.S. Pat. No. 4,328,722 disclosed the use of planetary gearing for radial adjustment of a tool, with the input to the planetary gearing coming from the rotatable spindle.
In more recent years, many machine tools have been equipped with tool changing mechanisms to change tools from a magazine into the operating spindle. The radial adjustment of such a boring tool on an interchangeable tool holder has also been suggested in U.S. Pat. No. 4,354,305. In this case, the radial adjustment was by a longitudinally movable central rod in the machine tool spindle. Also, in U.S. Pat. Nos. 4,447,177 and 4,451,185, radial adjustment was made by means of planetary gearing together with means to hold the ring gear stationary. In these latter two patents, the one input to the planetary gearing was from the machine tool spindle, and only minor adjustments in radial position were established because the tool holder had a slot to establish an effective hinge portion to permit slight bending movements of the cutting tool mount.